1. Field of the Invention
The present invention relates to a hydrogen generator, more particularly, in which electrodes and an electrolyte maintain a substantially constant contact area therebetween, thereby obtaining hydrogen generated during electrolysis of the electrolyte stably per a predetermined time.
2. Description of the Related Art
Recent years have seen an increasing use of small-sized electronic devices such as mobile phones, personal digital assistants (PDAs), digital cameras and laptop computers. Particularly, with the start of digital multimedia broadcasting (DMB) for mobile phones, a small-sized mobile terminal is required to be improved in power capacity.
A lithium-ion secondary battery in current general use has a capacity enabling about two hours of DMB viewing and has been performing better. However, as a more fundamental solution, there has been a growing expectation for a micro fuel cell reduced in size and capable of providing high-capacity power.
In general, the micro fuel cell adopts hydrogen as the most appropriate fuel for realizing high performance. This has led to a need for a device for generating hydrogen supplied to the micro fuel cell.
There are two ways to produce this fuel cell. One is a direct methanol method in which a hydrocarbon fuel such as methanol is directly supplied to a fuel electrode. The other is a reformed hydrogen fuel cell (RHFC) method in which hydrogen is extracted from methanol to be injected to a fuel electrode.
The RHFC method utilizes hydrogen as a fuel in the same manner as a polymer electrode membrane (PEM) method. Thus, the RHFC has advantages of high-output, high power capacity attainable per unit volume, and no reactant present other than water. However, the RHFC method requires an additional reformer to be installed in a system, thus hindering miniaturization.
Also, the reformer includes a vaporizer vaporizing a hydrocarbon liquid fuel into a gas phase, a reforming unit converting methanol as a fuel into hydrogen through catalytic reaction at a temperature of 250 to 350 and a CO remover (or CO2 remover) removing a CO gas (or CO2 gas), i.e., the byproduct accompanying the reforming reaction.
However, the reforming reaction in the reforming unit is an endothermic reaction where a reaction temperature is maintained at 250 to 350 . On the other hand, the reforming reaction in the CO remover is an exothermic reaction in which a reaction temperature is maintained at 170□ to 200□ . Therefore, to attain good reaction efficiency, the RHFC method necessitates an intricate high-temperature system, thereby complicating a structure of an overall fuel cell device and impeding reduction in manufacturing costs thereof.
Moreover, the RHFC method inevitably entails an additional structure for removing the CO gas or CO2 gas, i.e., the byproduct generated during the reforming reaction. This hinders reduction in an overall volume of the device and in manufacturing costs.
Meanwhile, as a method for generating hydrogen by electrolysis, as shown in FIG. 1, an electrolyte such as sea water is filled in an electrolytic bath 1 of a predetermined size. In the electrolytic bath 1 are immersed an anode electrode 2 formed of magnesium (Mg) more ionizable than hydrogen and a cathode electrode 3 formed of iron (Fe). The anode electrode 2 and the cathode electrode 3 are fixed to the electrolytic bath 1 and a cover 4 having a hydrogen outlet is provided on the electrolytic bath 1.
Here, when current is supplied to the anode electrode 2 and the cathode electrode 3, respectively, magnesium reacts with water according to equations 1, 2 and 3. In turn, magnesium hydroxide is generated in the electrolytic bath 1 to generate hydrogen according to equation 4.Mg→Mg+2+2e−  equation 12H2O→2OH−+2H+  equation 22H++2e−→H2  equation 3Mg+2H2O→Mg(OH)2+H2  equation 4
Also, the magnesium hydroxide obtained by the equations above remain in the electrolytic bath 1, while the hydrogen is exhausted outward through the hydrogen outlet 5 of the cover 4 to be utilized as a fuel.
However, while the hydrogen is generated by supplying the current to the anode electrode 2 and the cathode electrode 3 immersed in the electrolyte of the electrolytic bath 1, water is gradually consumed to lower a level of the electrolyte of the electrolytic bath 1, thereby reducing a contact area between the electrolyte and the electrodes.
Here, an amount of hydrogen generated in the electrolytic bath 1 is proportional to the contact area between the electrolyte and the electrodes. Thus, a fall in the level of the electrolyte of the electrolytic bath leads to a decrease in the amount of hydrogen generated.
This accordingly requires a sensor (not shown) for measuring the level of the electrolyte consumed in the electrolytic bath and a pump 6 replenishing the electrolytic bath 1 with an electrolyte tantamount to the consumed amount. In consequence, this hinders downsizing of the device and subsequent miniaturization thereof, and also increases manufacturing costs.